We propose to apply techniques of automated, computerized flow cytometry to analyse cellular immunologic processes in vivo and in vitro. Patients with allografts, breast cancer, renal disease and viral infections and animals during rejection of tumors and allografts will be studied with monoclonal antibodies to T cell subsets, B cells, monocytes, fibronectin and other cell surface markers. Human T-cell clones reactive to protein antigens and from patients with breast cancer will be selected and characterized. New monoclonal reagents to human and guinea pig T-cells and monocytes will be developed and used in these studies. Flow cytometry will be used to analyse the effects of the in vivo administration of monoclonal antibodies to T cells in humans, monkeys and guinea pigs. Innovations in histocompatibility typing and hormone receptor studies will be sought. The proposed instrument, a Spectrum III flow cytometer with a 2150 10Mb computer will be shared among major users at the Massachusetts General Hospital and will significantly enhance progress in the above studies. These studies should reveal new insights into basic and clinical immune mechanisms which will be relevant to transplantation, tumor resistance, viral illness and autoimune diseases.